Re: [PATCH v4 1/4] OvmfPkg/MemEncryptHypercallLib: add library to support SEV hypercalls.

["Brijesh Singh" <brijesh.singh@amd.com>]

On 6/22/2021 2:47 PM, Brijesh Singh wrote:
> 
> 
> On 6/21/2021 8:56 AM, Ashish Kalra wrote:
>> From: Ashish Kalra <ashish.kalra@amd.com>
>>
>> Add SEV and SEV-ES hypercall abstraction library to support SEV Page
>> encryption/deceryption status hypercalls for SEV and SEV-ES guests.
>>
>> Cc: Jordan Justen <jordan.l.justen@intel.com>
>> Cc: Laszlo Ersek <lersek@redhat.com>
>> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
>>
> Remove this newline.
> 
>> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
>> ---
>>  Maintainers.txt                                                      |   2 +
>>  OvmfPkg/Include/Library/MemEncryptHypercallLib.h                     |  43 ++++++++
>>  OvmfPkg/Library/MemEncryptHypercallLib/Ia32/MemEncryptHypercallLib.c |  37 +++++++
>>  OvmfPkg/Library/MemEncryptHypercallLib/MemEncryptHypercallLib.inf    |  42 ++++++++
>>  OvmfPkg/Library/MemEncryptHypercallLib/X64/AsmHelperStub.nasm        |  28 ++++++
>>  OvmfPkg/Library/MemEncryptHypercallLib/X64/MemEncryptHypercallLib.c  | 105 ++++++++++++++++++++
>>  OvmfPkg/OvmfPkgIa32.dsc                                              |   1 +
>>  OvmfPkg/OvmfPkgIa32X64.dsc                                           |   1 +
>>  OvmfPkg/OvmfPkgX64.dsc                                               |   1 +
>>  OvmfPkg/OvmfXen.dsc                                                  |   1 +
>>  10 files changed, 261 insertions(+)
>>
>> diff --git a/Maintainers.txt b/Maintainers.txt
>> index ea54e0b7e9..8ecc8464ba 100644
>> --- a/Maintainers.txt
>> +++ b/Maintainers.txt
>> @@ -449,8 +449,10 @@ F: OvmfPkg/AmdSev/
>>  F: OvmfPkg/AmdSevDxe/
>>  F: OvmfPkg/Include/Guid/ConfidentialComputingSecret.h
>>  F: OvmfPkg/Include/Library/MemEncryptSevLib.h
>> +F: OvmfPkg/Include/Library/MemEncryptHypercallLib.h
>>  F: OvmfPkg/IoMmuDxe/AmdSevIoMmu.*
>>  F: OvmfPkg/Library/BaseMemEncryptSevLib/
>> +F: OvmfPkg/Library/MemEncryptHypercallLib/
>>  F: OvmfPkg/Library/PlatformBootManagerLibGrub/
>>  F: OvmfPkg/Library/VmgExitLib/
>>  F: OvmfPkg/PlatformPei/AmdSev.c
>> diff --git a/OvmfPkg/Include/Library/MemEncryptHypercallLib.h b/OvmfPkg/Include/Library/MemEncryptHypercallLib.h
>> new file mode 100644
>> index 0000000000..b241a189b6
>> --- /dev/null
>> +++ b/OvmfPkg/Include/Library/MemEncryptHypercallLib.h
>> @@ -0,0 +1,43 @@
>> +/** @file
>> +
>> +  Define Secure Encrypted Virtualization (SEV) hypercall library.
>> +
>> +  Copyright (c) 2020, AMD Incorporated. All rights reserved.<BR>
>                    ^^^^
>                    2021
> 
>> +
>> +  SPDX-License-Identifier: BSD-2-Clause-Patent
>> +
>> +**/
>> +
>> +#ifndef _MEM_ENCRYPT_HYPERCALL_LIB_H_
>> +#define _MEM_ENCRYPT_HYPERCALL_LIB_H_
>> +
>> +#include <Base.h>
>> +
>> +#define KVM_HC_MAP_GPA_RANGE   12
>> +#define KVM_MAP_GPA_RANGE_PAGE_SZ_4K    0
>> +#define KVM_MAP_GPA_RANGE_PAGE_SZ_2M    (1 << 0)
>> +#define KVM_MAP_GPA_RANGE_PAGE_SZ_1G    (1 << 1)
>> +#define KVM_MAP_GPA_RANGE_ENC_STAT(n)   ((n) << 4)
>> +#define KVM_MAP_GPA_RANGE_ENCRYPTED     KVM_MAP_GPA_RANGE_ENC_STAT(1)
>> +#define KVM_MAP_GPA_RANGE_DECRYPTED     KVM_MAP_GPA_RANGE_ENC_STAT(0)
>> +
>> +/**
>> + This hyercall is used to notify hypervisor when a page is marked as
>> + 'decrypted' (i.e C-bit removed).
>> +
> Looking at the function signature it seems this routine is used for both set
> and clear. Please update the comment accordingly.
> 
> 
>> + @param[in]   PhysicalAddress       The physical address that is the start address
>> +                                    of a memory region.
>> + @param[in]   Length                The length of memory region
>> + @param[in]   Mode                  SetCBit or ClearCBit
>> +
>> +**/
>> +
>> +VOID
>> +EFIAPI
>> +SetMemoryEncDecHypercall3 (
>> +  IN  UINTN     PhysicalAddress,
>> +  IN  UINTN     Length,
>> +  IN  UINTN     Mode
>> +  );
>> +
>> +#endif
>> diff --git a/OvmfPkg/Library/MemEncryptHypercallLib/Ia32/MemEncryptHypercallLib.c b/OvmfPkg/Library/MemEncryptHypercallLib/Ia32/MemEncryptHypercallLib.c
>> new file mode 100644
>> index 0000000000..2e73d47ee6
>> --- /dev/null
>> +++ b/OvmfPkg/Library/MemEncryptHypercallLib/Ia32/MemEncryptHypercallLib.c
>> @@ -0,0 +1,37 @@
>> +/** @file
>> +
>> +  Secure Encrypted Virtualization (SEV) hypercall helper library
>> +
>> +  Copyright (c) 2020, AMD Incorporated. All rights reserved.<BR>
>                    ^^^^
>                    2021
> 
>> +
>> +  SPDX-License-Identifier: BSD-2-Clause-Patent
>> +
>> +**/
>> +
>> +#include <Uefi.h>
>> +#include <Uefi/UefiBaseType.h>
>> +#include <Library/BaseLib.h>
>> +
>> +/**
>> + This hyercall is used to notify hypervisor when a page is marked as
>> + 'decrypted' (i.e C-bit removed).
>> +
>> + @param[in]   PhysicalAddress       The physical address that is the start address
>> +                                    of a memory region.
>> + @param[in]   Length                The length of memory region
>> + @param[in]   Mode                  SetCBit or ClearCBit
>> +
>> +**/
>> +
>> +VOID
>> +EFIAPI
>> +SetMemoryEncDecHypercall3 (
>> +  IN PHYSICAL_ADDRESS PhysicalAddress,
>> +  IN UINTN            Pages,
>> +  IN UINTN            Mode
>> +  )
>> +{
>> +  //
>> +  // Memory encryption bit is not accessible in 32-bit mode
>> +  //
>> +}
>> diff --git a/OvmfPkg/Library/MemEncryptHypercallLib/MemEncryptHypercallLib.inf b/OvmfPkg/Library/MemEncryptHypercallLib/MemEncryptHypercallLib.inf
>> new file mode 100644
>> index 0000000000..a77d58a7e6
>> --- /dev/null
>> +++ b/OvmfPkg/Library/MemEncryptHypercallLib/MemEncryptHypercallLib.inf
>> @@ -0,0 +1,42 @@
>> +## @file
>> +#  Library provides the hypervisor helper functions for SEV guest
>> +#
>> +# Copyright (c) 2020 Advanced Micro Devices. All rights reserved.<BR>
>                    ^^^^
>                    2021
>> +#
>> +#  SPDX-License-Identifier: BSD-2-Clause-Patent
>> +#
>> +#
>> +##
>> +
>> +[Defines]
>> +  INF_VERSION                    = 1.25
>> +  BASE_NAME                      = MemEncryptHypercallLib
>> +  FILE_GUID                      = 86f2501e-f128-45f3-91c4-3cff31656ca8
>> +  MODULE_TYPE                    = BASE
>> +  VERSION_STRING                 = 1.0
>> +  LIBRARY_CLASS                  = MemEncryptHypercallLib
>> +
>> +#
>> +# The following information is for reference only and not required by the build
>> +# tools.
>> +#
>> +# VALID_ARCHITECTURES           = IA32 X64
>> +#
>> +
>> +[Packages]
>> +  MdeModulePkg/MdeModulePkg.dec
>> +  MdePkg/MdePkg.dec
>> +  UefiCpuPkg/UefiCpuPkg.dec
>> +  OvmfPkg/OvmfPkg.dec
>> +
>> +[Sources.X64]
>> +  X64/MemEncryptHypercallLib.c
>> +  X64/AsmHelperStub.nasm
>> +
>> +[Sources.IA32]
>> +  Ia32/MemEncryptHypercallLib.c
>> +
>> +[LibraryClasses]
>> +  BaseLib
>> +  DebugLib
>> +  VmgExitLib
>> diff --git a/OvmfPkg/Library/MemEncryptHypercallLib/X64/AsmHelperStub.nasm b/OvmfPkg/Library/MemEncryptHypercallLib/X64/AsmHelperStub.nasm
>> new file mode 100644
>> index 0000000000..f29b96f9b0
>> --- /dev/null
>> +++ b/OvmfPkg/Library/MemEncryptHypercallLib/X64/AsmHelperStub.nasm
>> @@ -0,0 +1,28 @@
>> +DEFAULT REL
>> +SECTION .text
>> +
>> +; VOID
>> +; EFIAPI
>> +; SetMemoryEncDecHypercall3AsmStub (
>> +;   IN UINT HypercallNum,
>> +;   IN INTN Arg1,
>> +;   IN INTN Arg2,
>> +;   IN INTN Arg3
>> +;   );
>> +global ASM_PFX(SetMemoryEncDecHypercall3AsmStub)
>> +ASM_PFX(SetMemoryEncDecHypercall3AsmStub):
>> +  ; UEFI calling conventions require RBX to
>> +  ; be nonvolatile/callee-saved.
>> +  push rbx
>> +  ; Copy HypercallNumber to rax
>> +  mov rax, rcx
>> +  ; Copy Arg1 to the register expected by KVM
>> +  mov rbx, rdx
>> +  ; Copy Arg2 to register expected by KVM
>> +  mov rcx, r8
>> +  ; Copy Arg2 to register expected by KVM
>> +  mov rdx, r9
>> +  ; Call VMMCALL
>> +  vmmcall
>> +  pop rbx
>> +  ret
>> diff --git a/OvmfPkg/Library/MemEncryptHypercallLib/X64/MemEncryptHypercallLib.c b/OvmfPkg/Library/MemEncryptHypercallLib/X64/MemEncryptHypercallLib.c
>> new file mode 100644
>> index 0000000000..1c09ea012b
>> --- /dev/null
>> +++ b/OvmfPkg/Library/MemEncryptHypercallLib/X64/MemEncryptHypercallLib.c
>> @@ -0,0 +1,105 @@
>> +/** @file
>> +
>> +  Secure Encrypted Virtualization (SEV) hypercall helper library
>> +
>> +  Copyright (c) 2020, AMD Incorporated. All rights reserved.<BR>
>                    ^^^^
>                    2021
>> +
>> +  SPDX-License-Identifier: BSD-2-Clause-Patent
>> +
>> +**/
>> +
>> +#include <Uefi.h>
>> +#include <Uefi/UefiBaseType.h>
>> +#include <Library/BaseLib.h>
>> +#include <Library/DebugLib.h>
>> +#include <Library/VmgExitLib.h>
>> +#include <Register/Amd/Ghcb.h>
>> +#include <Register/Amd/Msr.h>
>> +#include <Library/MemEncryptSevLib.h>
>> +#include <Library/MemEncryptHypercallLib.h>
>> +
>> +//
>> +// Interface exposed by the ASM implementation of the core hypercall
>> +//
>> +//
>> +
>> +VOID
>> +EFIAPI
>> +SetMemoryEncDecHypercall3AsmStub (
>> +  IN  UINTN  HypercallNum,
>> +  IN  UINTN  PhysicalAddress,
>> +  IN  UINTN  Length,
>> +  IN  UINTN  Mode
>> +  );
>> +
> The function signature does not match with documented signature. Fix the
> SetMemoryEncDecHypercall3AsmStub() documented in AsmHelperStub.nasm to use
> UINTN.
> 
> 
>> +STATIC
>> +VOID
>> +GhcbSetRegValid (
>> +  IN OUT GHCB       *Ghcb,
>> +  IN GHCB_REGISTER  Reg
>> +  )
>> +{
>> +  UINT32  RegIndex;
>> +  UINT32  RegBit;
>> +
>> +  RegIndex = Reg / 8;
>> +  RegBit   = Reg & 0x07;
>> +
>> +  Ghcb->SaveArea.ValidBitmap[RegIndex] |= (1 << RegBit);
>> +}
>> +
> 
> This looks similar to VmgSetOffsetValid().
> 
>> +/**
>> + This hyercall is used to notify hypervisor when a page is marked as
>> + 'decrypted' (i.e C-bit removed).
>> +Please update the comment.
> 
>> + @param[in]   PhysicalAddress       The physical address that is the start address
>> +                                    of a memory region.
>> + @param[in]   Length                The length of memory region
>> + @param[in]   Mode                  SetCBit or ClearCBit
>> +
>> +**/
>> +
>> +VOID
>> +EFIAPI
>> +SetMemoryEncDecHypercall3 (
>> +  IN PHYSICAL_ADDRESS PhysicalAddress,
>> +  IN UINTN            Pages,
>> +  IN UINTN            Mode
>> +  )
>> +{
>> +  if (MemEncryptSevEsIsEnabled ()) {> +    MSR_SEV_ES_GHCB_REGISTER  Msr;
>> +    GHCB                      *Ghcb;
>> +    BOOLEAN                   InterruptState;
>> +    UINT64                    Status;
>> +
>> +    Msr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);
>> +    Ghcb = Msr.Ghcb;
>> +
>> +    VmgInit (Ghcb, &InterruptState);
>> +
>> +    Ghcb->SaveArea.Rax = KVM_HC_MAP_GPA_RANGE;
>> +    GhcbSetRegValid (Ghcb, GhcbRax);
>> +    Ghcb->SaveArea.Rbx = PhysicalAddress;
>> +    GhcbSetRegValid (Ghcb, GhcbRbx);
>> +    Ghcb->SaveArea.Rcx = Pages;
>> +    GhcbSetRegValid (Ghcb, GhcbRcx);
>> +    Ghcb->SaveArea.Rdx = Mode;
>> +    GhcbSetRegValid (Ghcb, GhcbRdx);
>> +    Ghcb->SaveArea.Cpl = AsmReadCs() & 0x3;
>> +    GhcbSetRegValid (Ghcb, GhcbCpl);
>> +
>> +    Status = VmgExit (Ghcb, SVM_EXIT_VMMCALL, 0, 0);
>> +    if (Status) {
>> +      DEBUG ((DEBUG_ERROR, "SVM_EXIT_VMMCALL failed %lx\n", Status));
> 
> You need to issue an SEV-ES guest termination vmexit followed by a deadloop to ensure
> that boot does not proceed.
> 
> You probably also need to check for the RAX register for the return code.
> 
> 
>> +    }
>> +    VmgDone (Ghcb, InterruptState);
>> +  } else {
>> +    SetMemoryEncDecHypercall3AsmStub (
>> +      KVM_HC_MAP_GPA_RANGE,
>> +      PhysicalAddress,
>> +      Pages,
>> +      Mode
>> +      );
> 
> How do you know whether the hyperviosr supports the Live migration ? In other
> words, is it safe to call the HC without knowing if HV supports the feature ?
> 

I see that in patch#4 you are adding a support to query the HV features flag
to determine whether HV supports the Live migration. You probably need to
pull that function into this library and and check the feature flag before
invoking HC.

This library can also export the function for others to use. You can cache
the value on the first call (similar to how BaseMemEncryptSevLib does for
the MemEncryptSevIsEnabled).


> Also, what will happen if we pass a bogus GPA. Does the HC return an error ?
> Same as SEV-ES block, you probably need to check the RAX register for the
> return code. On failure, cause an assert() and terminate the boot.
> 
> 
>> +  }
>> +}
>> diff --git a/OvmfPkg/OvmfPkgIa32.dsc b/OvmfPkg/OvmfPkgIa32.dsc
>> index f53efeae79..36f1d82ce7 100644
>> --- a/OvmfPkg/OvmfPkgIa32.dsc
>> +++ b/OvmfPkg/OvmfPkgIa32.dsc
>> @@ -176,6 +176,7 @@
>>    VirtioLib|OvmfPkg/Library/VirtioLib/VirtioLib.inf
>>    LoadLinuxLib|OvmfPkg/Library/LoadLinuxLib/LoadLinuxLib.inf
>>    MemEncryptSevLib|OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf
>> +  MemEncryptHypercallLib|OvmfPkg/Library/MemEncryptHypercallLib/MemEncryptHypercallLib.inf
>>  !if $(SMM_REQUIRE) == FALSE
>>    LockBoxLib|OvmfPkg/Library/LockBoxLib/LockBoxBaseLib.inf
>>  !endif
>> diff --git a/OvmfPkg/OvmfPkgIa32X64.dsc b/OvmfPkg/OvmfPkgIa32X64.dsc
>> index b3662e17f2..2a743688b4 100644
>> --- a/OvmfPkg/OvmfPkgIa32X64.dsc
>> +++ b/OvmfPkg/OvmfPkgIa32X64.dsc
>> @@ -180,6 +180,7 @@
>>    VirtioLib|OvmfPkg/Library/VirtioLib/VirtioLib.inf
>>    LoadLinuxLib|OvmfPkg/Library/LoadLinuxLib/LoadLinuxLib.inf
>>    MemEncryptSevLib|OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf
>> +  MemEncryptHypercallLib|OvmfPkg/Library/MemEncryptHypercallLib/MemEncryptHypercallLib.inf
>>  !if $(SMM_REQUIRE) == FALSE
>>    LockBoxLib|OvmfPkg/Library/LockBoxLib/LockBoxBaseLib.inf
>>  !endif
>> diff --git a/OvmfPkg/OvmfPkgX64.dsc b/OvmfPkg/OvmfPkgX64.dsc
>> index 0a237a9058..eb9da51a15 100644
>> --- a/OvmfPkg/OvmfPkgX64.dsc
>> +++ b/OvmfPkg/OvmfPkgX64.dsc
>> @@ -180,6 +180,7 @@
>>    VirtioLib|OvmfPkg/Library/VirtioLib/VirtioLib.inf
>>    LoadLinuxLib|OvmfPkg/Library/LoadLinuxLib/LoadLinuxLib.inf
>>    MemEncryptSevLib|OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf
>> +  MemEncryptHypercallLib|OvmfPkg/Library/MemEncryptHypercallLib/MemEncryptHypercallLib.inf
>>  !if $(SMM_REQUIRE) == FALSE
>>    LockBoxLib|OvmfPkg/Library/LockBoxLib/LockBoxBaseLib.inf
>>  !endif
>> diff --git a/OvmfPkg/OvmfXen.dsc b/OvmfPkg/OvmfXen.dsc
>> index 3c1ca6bfd4..de0c052832 100644
>> --- a/OvmfPkg/OvmfXen.dsc
>> +++ b/OvmfPkg/OvmfXen.dsc
>> @@ -167,6 +167,7 @@
>>    QemuFwCfgLib|OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgDxeLib.inf
>>    QemuLoadImageLib|OvmfPkg/Library/GenericQemuLoadImageLib/GenericQemuLoadImageLib.inf
>>    MemEncryptSevLib|OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf
>> +  MemEncryptHypercallLib|OvmfPkg/Library/MemEncryptHypercallLib/MemEncryptHypercallLib.inf
>>    LockBoxLib|OvmfPkg/Library/LockBoxLib/LockBoxBaseLib.inf
>>    CustomizedDisplayLib|MdeModulePkg/Library/CustomizedDisplayLib/CustomizedDisplayLib.inf
>>    FrameBufferBltLib|MdeModulePkg/Library/FrameBufferBltLib/FrameBufferBltLib.inf
>>
> Update the AmdSev.dsc to include this library.
> 
> 
> -Brijesh
>